Sintered steel particles containing dispersed carbides

ABSTRACT

THE INVENTION RELATES GENERALLY TO POWDERED METAL ARTICLES AND METHOD FOR PRODUCING THE SAME. IN MORE PARTICULAR ASPECTS, THE INVENTION RELATES TO POWDERED METAL ARTICLES PRODUCED FROM HIGH SPEED TOOL AND DIE STEEL COMPOSITIONS BY HOT COMPACTING PARTICLES OF SAID COMPOSITIONS. THE PARTICLES RANGE IN SIZE FROM ABOUT -30 OR FINER STANDARD MESH AND CONTAIN A REACTIVE METAL COMPONENT SUCH AS TITANIUM, VANADIUM, ZIROCONIUM, COLUMBIUM, MOLYBDENUM, TUNGSTEN OR TANTALUM. THE REACTIVE METAL COMPONENT IS REACTED WITH A NON-METAL, WHICH MAY BE CARBON, OXYGEN OR NITROGEN, TO PRODUCE A NONMETALLIC DISPERSION OF SAID REACTIVE METAL AND NON-METAL. THE ARTICLE IS CAPABLE OF HARDENING TREATMENT BY CONVENTIONAL AUSTENITIZING, QUENCHING AND TEMPERING TO HARDNESS LEVELS ABOVE ABOUT 58 RC FOR DIE STEEL AND 64 RC FOR HIGH SPEED STEELS. AUSTENITIZING TO THESE HIGH HARDNESS LEVELS MAY BE ACHIEVED IN VERY SHORT TIMES ON THE ORDER OF TWO MINUTES OR LESS. IN ADDITION DURING HARDENING TREATMENT THE SYMMETRY OR OUT-OF-ROUNDNESS OF THE ARTICLE REMAINS SUBSTANTIALLY UNCHANGED.

SINTERED STEEL PARTICLES CONTAINING DISPERSED CARBIDES Filed Sept. 11, 1967 G. STEVEN Feb. 9, 1971 3 Sheets-Sheet 1 PARTICLE METALLURGY COMPACT PARTICLE ME TALLURG Y COMPACT RES/DUAL AND T RANSF OPMED RESIDUAL AND T RANSF ORMEO CARE/DES CLOSE TO THE EDGE CARE/DES IN THE CENTER FIG /5 FIG. IA

f A, gm M COMMERCIAL BA]? PROOUC T M/OPA O/US FIG: 2

INVENTOR GAR) STEVEN Attorney Feb. 9, 1971 G STEVEN 35mm SINTERED STEEL PARTICLES CONTAINING DISPERSED CARBIDES Filed Sept. 11. 1967 5 Sheets-Sheet 2 K 66 POWDER COMPACT QC A/ a b. a 65 Q A COMMERCIAL BAR INVENTOR. GARY STEVE/V A r farney Feb. 9, 1971 STEVEN 3561334 SINTERED STEEL PARTICLES CONTAINING DISPERSED CARBIDES Filed Sept. 11, 1967 5 Sheets-Sheet 5 PARTICLE PART/CLE ME TALLURGY COMPACT ME TALLURGY COMPACT CENTER OF 5 BY IIIVCH EDGE OF 5 8) [INCH COMPACT C OMPAC T F I 6 44 F I G 45 COMMERCIAL BAR PRODUCT COMMERCIAL BAR PRODUCT M/DRADIUS OF 6 INCH M/DRAO/US OF 9 INCH DIAMETER ROU I VO DIAMETER ROUND F 61 5A F 6. 5B

IIVVE/V TOR GARY STEVEN Unite 6 Claims ABSTRACT OF THE DISCLQSURE The invention relates generally to powdered'metal articles and method for producing the same. In more particular aspects, the invention relates to powdered metal articles produced from high speed tool and die steel compositions by hot compacting particles of said compositions. The particles range in size from about -30 or finer standard mesh and contain a reactive metal component such as titanium, vanadium, zirconium, columbium, molybdenum, tungsten or tantalum. The reactive metal component is reacted with a non-metal, which may be carbon, oxygen or nitrogen, to produce a nonmetallic dispersion of said reactive metal and non-metal. The article is capable of hardening treatment by conventional austenitizing, quenching and tempering to hardness levels above about 58 R for die steels and 64 R for high speed steels. Austenitizing to these high hardness levels may be achieved in very short times on the order of two minute or less. In addition during hardening treatment the symmetry or out-of-roundness of the article remains substantially unchanged.

In the manufacture of articles from high speed tool and die steels, such as cutting tools, dies and the like, it is desirable to provide an initially relatively soft article that may be readily machined. In the case of cutting tools, the machining operation is used to produce the required cutting edge whereas, in the case of dies it is advantageous to machine the die blank while the same is in a relatively soft condition. After the machining operation, the article whether it be a tool or die is given a hardening treatment comprising austenitizing, quenching and tempering to the desired high hardness level. In these high speed steels, it is also advantageous and in many applications a strict requirement that upon austenitizing, quenching and tempering the dimensions of the article remain uniform after treatment. For example, in the case of a cutting tool such as a cylindrical hob, any change in symmetry or out-of-roundness after the hardening treatment would require a subsequent grinding operation. In the case of a die where specified tolerances usually must be maintained, any nonuniformity in size after hardening treatment would also have to be in some measure corrected by additional grinding. In both the case of cutting tools and dies, this grinding operation after hardening treatment is rendered more ditficult and expensive because of the increased hardness of the material.

In the case of a cutting tool this grinding is also known to shorten the tool life. Therefore, the importance of obtaining articles of this type that are characterized by the substantial absence of nonuniformity in size upon austenitizing, quenching and tempering is obivous. It has been found, as will be shown and explained in greater detail hereinafter, that out-of-roundness after hardening treatment is a function of carbide alignment or orientation. More specifically, the presence of directionally oriented carbide stringers has been shown to cause an out-of-roundness in articles, after hardening treatment, in the direction of said stringers. In contrast, in the prestes at ence of a uniformly dispersed, nondirectional, homogeneous, fine carbide structure, the problem of out-ofroundness after hardening treatment is substantially eliminated. By providing a fine, uniformly dispersed carbide structure, the austenitizing times necessary to achieve the required high hardness levels are substantially shortened which improves the economics of the treatment.

As mentioned hereinabove, both tool and die articles must be subjected to a machining operation during the course of manufacture. To permit easy machining, and particularly with cutting tools, maintenance of the machined cutting edge during use, it is desirable to have a relatively fine-grained micro-structure in the final article.

It is accordingly the primary object of the present invention to provide high speed tool and die steel articles and a method for manufacturing the same that are superior in both product quality and economy of manufacture than conventional articles of this type.

A more specific object of the invention is to provide tool and die steel articles produced from metal particles by a powder metallurgy technique, whereby improved properties and economies of manufacture are achieved.

Another object of the invention is to provide articles of high speed tool or die steel that are subject to substantially no out-of-roundness, or loss of symmetry after hardening treatment by conventional austenitizing, quenching and tempering.

A further, more specific object of the invention is to provide hot-compacted articles of high speed tool and die steel particles that are characterized by a hardness of at least about 58 R for die steels and 64 R for high speed steels and a substantially uniform dispersion of carbon, oxygen or nitrogen nonmetallic compounds.

Yet another object of the invention is to provide a hotcompacted article of high speed tool steel, such as a cylindrical hob or die, wherein all the machining and finishing operation of the article may be done prior to hardening by austenitizing, quenching and tempering; thi may be accomplished because the article is not subject to any substantial change of symmetry or nonuniform dimensional change as a result of the hardening treatment.

These and other objects as well as a complete understanding of the invention may be obtained from the following description and drawings, in which:

FIGS. 1A and 1B are photomicrographs showing annealed longitudinal microstructures of compacts of M28 tool steel in accordance with the present invention;

FIG. 2 is a photomicrograph showing the microstructure of a slice cut from a conventional bar of material of the same composition and size as that of the compacts of FIGS. 1A and 113;

FIG. 3 is a graph comparing the austenitizing times required to achieve various hardnesses with campacts in accordance with the invention and samples of conventional material, all samples being austenitized at 2200 F., oil quenched and tempered 2+2+2 hours at 1025 F.

FIGS. 4A and 4B are photomicrographs of samples in accordance with the invention; and

FIGS. 5A and 5B are photomicrographs of samples of conventional bar products of the same composition as the samples of FIGS. 4A and 4B.

In the broader aspects of the invention, particles of a high speed toolor die-steel composition containing a metal component capable of reacting with a non-metal, such as carbon, oxygen or nitrogen, are provided. Each of the particles has a non-metallic compound of the reactive metal and non-metal such as carbides, nitrides or oxides substantially evenly dispersed throughout the particle. A charge of the metal particles is heated preferably in the substantial absence of oxygen to an elevated temperature and is then subjected to pressure application to compact the same in accordance with any suitable powder metallurgy technique to a final density of at least about 99 percent. For example, the compacting and heating of the particles may be achieved by placing the same in an evacuated envelope or container which is heated to temperature in a furnace and then placed in a die wherein the pressure necessary for compacting is applied by the use of a ram; alternately, the envelope containing the powdered metal charge to be compacted may be placed in a fluidpressure vessel, commonly termed an autoclave, for compacting and the charge may be heated either in the autoclave or in a furnace prior to being placed in the autoclave. Unless deliberate oxide additions are desired, the heating and compacting operation can be conducted in the substantial absence of oxygen to insure the maintenance of an oxide-free particle surface for the purpose of good particle bonding during compacting and the maintenance of final product cleanliness.

The size of the particles of the high speed tool or die steel used in the practice of the invention preferably should be in the size range of standard mesh or finer. The particle size influences the ultimate carbide size characterizing the final product.

Although the invention has great utility with all high speed tooland die-steel compositions containing a metal component capable of reacting with a non-metal, such as carbon, oxygen and nitrogen to form a nonmetallic compound thereof, it is particularly advantageous with alloys within the composition range set forth in Table I. Suitable reactive metals are titanium, vanadium, zirconium, columbium, molybdenum, tungsten and tantalum.

With tungsten plus molybdenum plus chromium plus vanadium equal to at least 10% of the total weight.

Examples of conventional, commercial high speed tool steels with which the invention may be used are listed in the following Table II:

4 addition, the presence of large carbides can impair the grindability of the product, whether it be a tool steel article or a die.

The grain size of the article may typically be 12 Snyder-Graft or finer. This fine grain size is believed to contribute toughness to the article. By the manufacture of the articles by powder metallurgy techniques, it is possible to exercise otherwise unobtainable control with respect to grain size. In conventional articles of the type to which the invention is directed, the grain size is almost completely dependent upon the amount of working imparted to the article. Hence, in the case of a tool steel article such as a hob, the larger the diameter of the hob and consequently the less working imparted thereto, the coarser would be the grain structure thereof. With the articles of the present invention, however, the grain size is completely independent of the size of the article.

As mentioned hereinabove, in the high speed tool or die steel articles to which the invention is directed, it is desirable to achieve high hardness levels by austenitizing, quenching and tempering. This is of particular importance in the case of tool steel articles wherein a hardness of about 58 R for die steels and 64 R or higher for high speed steels is required. This is achieved with the articles of the invention as described above by an austenitizing time at a temperature not longer than two minutes. The short austenitizing time for the reasons advanced hereinabove is beneficial.

The articles of the invention are characterized further by a homogeneous, non-directional carbide structure. It has been demostrated, as will be shown in detail hereinafter, that change in symmetry, shape, or out-of-roundness is a direct function of the directionality of the carbide structure. Specifically, upon austenitizing, quenching and tempering, the article will tend to change in size in the direction of carbide orientation. This is substantially eliminated with the present invention because of the homogeneous, non-directional carbide structure. This homogeneous, non-directional carbide structure provides an additional benefit in certain cutting tool applications in that a cutting tool may be cut from cutting-tool stock produced in accordance with the present invention without necessitating cutting the stock in a direction such that the direction of carbide stringers is substantially normal to the cutting edge of the tool. In conventional practice, if this requirement is not maintained, it is possible for an elongated carbide to be present along the cutting edge of the tool. A carbide in such a location would, of course,

TABLE II 0, Mn, Si, Cr, V, W, o, 00, M percent; percent percent percent percent porcont percent percent AISI designation T 30 30 4 1. 15 75 30 30 4 1. 15 3O 30 4 2 30 30 8. 75 1. 15 1. 00 30 30 4. 15 1. 85 30 30 4. l5 1. 95 1. 05 30 30 4 2. 4

1 All of these compositions may be sulfurized to improve machinability.

With the articles of the invention, the average carbide size is desirably 5 microns maximum and preferably 1 to 2 microns. Large carbides may necessitate austenitizing times at temperatures that are excessive and therefore uneconomical. It has been found that the average carbide size of 5 microns maximum is desirable to achieve the desired hardness in high speed steels of 64 R and greater depending upon the specific metallurgical composition of the steel, at austenitizing times at temperature of two minutes or less. In addition, in cutting-tool applications the presence of large carbides, which may be present in cutting edges of the tools, may cause increased chipping of the cutting edges during use of the tool. In

chip away causing attendant dulling of the cutting edge after only short use of the tool. Hence, by permitting a tool to be cut from stock in any direction without regard to carbide directionality, maximum utilization of tool stock material may be made. In brief, it may be seen that the commonly used terminology of longitudinal and transverse properties with respect to tool steel articles becomes nonexistent by the application of the present invention.

As will be demonstrated in detail hereinafter, the maximum size change or out-of-roundness upon austenitizing, quenching and tempering of a typical 3-inch diameter hob in accordance With the invention is only 0.0001

inch which is regarded as substantially no size change. In contrast, a conventional hob of this diameter would typically exhibit an out-of-roundness on the order of 0.0008 inch or more.

The nonmetallic compounds of the reactive metal and the carbon, oxygen or nitrogen, as described hereinabove, may be produced in the high speed tool or die steel particles by either of two practices. First, the nonmetallic product may be present in the melt from which the particles are made. Second, the particles may be manufactured in the substantially pure reactive metal form and thereafter the non-metal may be reacted with the reactive metal by placing the particles in an environment of said non-metal, e.g., carbon, oxygen or nitrogen environment causing the reaction to take place, and thereafter diffusing the' nonmetallic reaction compound substantially uniformly throughout the particle.

Although, as explained hereinabove, the invention has wide application in the area of high speed tool and die steel products, it has been found to be especially suited to the production of hobs of high speed tool steel. A hob is a cylindrical, rotating cutting tool having helical before the hob has been hardened as by austenitizing, quenching, and tempering. Prior to this invention, during the hardening treatment the hob would become unsymmetrical or be characterized by out-of-roundness. This necessitated, after hardening treatment, a grinding operation to return the cylindrical hob blank to the required symmetry. In contrast, with the present invention, the homogeneous, nondirectional carbide structure and the resulting absence of substantial out-of-roundness upon hardening treatment eliminate the need for grinding to return the hob to symmetry after the hardening treatment. It is well known that such grinding adversely affects tool life.

As a specific example of the practice of the invention, high-carbon M high speed steel was used in accordance with the present invention in the manufacture of'bars from 3 to 6 inches in diameter, which are of the type used extensively for conventional gear hobs and special end mill cutters. The composition of the steel from which these bars were made as well as that of a commercial 5-inch diameter bar used for comparison purposes is presented in Table III:

TABLE III.-CHEMICAL COMPOSITIONS OF COMMERCIAL AND PARTICLE COMPACTED 0.9 TO 1.10 %CARBON M25 HIGH SPEED STEELS EVALUATED Chemical composition, percent l Commercial steel IIt 23,883, 15 ton.

splined teeth along its surface. It is used for forming,

Table IV describes the preparation of the metal parby a milling operation, gear teeth, spline keys and the 40 ticles and vacuum hot-pressing cycles for the compacts like. The cutting action is achieved by rotating the hob While feeding the same into the workpiece. The flutes of 299-58 and 300-54 of the compositions set forth in Table III.

TABLE IV.POWDER PREPARATION AND VACUUM HOTCOMPACTING CONDITIONS OF COMPAC'IS Procedure and conditions Preparation Compact 209-58 Compact 300-54 Additional powder preparation Cleaned 1 hour in NaOH; cleaned sonically Tumbled with steel balls, cleaned sonically in chromic acid. in chromic acid, screened out325 mesh Powder addition 0.05% lampblack 0.2% lampblack.

Vacuum hot-pressing sequences Heated the powder Filled 4 inch diameter by 6 inch high can with powder 1 Fill in a 6 inch-diameter by 6 inch high evacuated can at 2,275 F. (Can developed a leak during soaking period: this leak was repaired prior-to repressing.) Rehcated at 2,200 F. for 115 minutes and repressed. Annealed 20 hours at 1.350 F..

air cooled Machined compact to 6% inch diameter. Covered all machined surfaces with stainless sheet and welded can shut. Soaked compact 2 hours at 2,275 F., pressed at 200 tons and annealed at 1,350 F., 16 hours followed by air cooling.

2 Baked canned assembly 2 hours at 1,100 F. Turned vacuum pump on for 2 hours. Transferred can to furnace at 2.225" F.\'acuu1n pump shut off for minutes; vacuum pump turned on again; pressure lowered inside can to 10 min. mercury; held for 200 minutes. Pressed with 200 tons repressed at 2,275 F.; annealed 16 hours at 1,350 F., air cooled. Turned to remove canning material 5 inches diameter by 1%; inch.

the hob provide the cutting action during this operation. no

The cutting ability of a hob, which is its most important property, has been found to be most adversely affected by tooth edge-crumbling. The degree of tooth edge-crumbling is to a large extent governed by the size and orientation of the carbides present in the hob, particularly at the tooth edges. If, for example, an elongated carbide is oriented longitudinally along a cutting tooth edge, this portion of the cutting tooth will readily break-away during cutting. It may be seen therefore that the fine, uniformly dispersed homogeneous carbide structure characterizing articles in accordance with the present invention is of great benefit in the particular application of hobs. In addition, during hob manufacture the cutting teeth of the hob must be machined into the surface of the cylindrical hob blank. This operation is performed In the experimental work described hereinafter. these compacts were compared with slices cut from a 5-inch diameter commercial bar of the high carbon MZS composition (6l338) listed in Table III. Specifically, the microstructures Were investigated. In addition, the samples were tested for machinability (as-annealed), transverse C- notch impact resistance and comparative cutting tool performance of lathe tool bits. Also, the radial size changes of samples from the compacts (4%" O.D.-1 A1" ID.- 2' thick) after being subjected to a conventional hardening sequence were determined. The compacts identified as 29958 and 30054 in Tables III and IV had a hardness after compacting of 32 R The annealing cycles used these samples as well as the conventional sample 6l338 was a full anneal at 1600 F., furnace cooled at 25 F. per hour to 1200 F. and air cooled to room temperature. As shown in FIGS. 1A and 1B, the annealed microstructures of the 5-inch diameter compacts have a fine, even distribution of residual carbides edge-to-center. In contrast, as shown in FIG. 2, the sample 61-33 8, which represents commercial product, shows extremely heavy segregation of relatively larger residual carbides at its mid-radius location. It is obvious from a comparipresence of increased section size. The relative eifect of these differing structures with respect to austentizing time required to achieve full hardness has been explained hereinabove. The effect of this structure with respect to loss of symmetry or out-of-roundness will be demonstrated hereinafter. The Charpy C-notch impact resistance of the samples is demonstrated in Table VI.

TABLE VI.CHARPY C-NOTCH IMPACT RESISTANCE OF VACUUM HOT-PRESSED AND COMMERCIAL 1.0% CARBON MZS Hardness, Charpy C-uotch Specimen Heat treatment R impact, it.-1b.

1.0% Rex M2S 1 2,200 F./4 min, 0.q.; tempered 66.0 3, 3, 3, 3, 2, 2 (average, 3)

1,025 I i/2+2 hrs. plus 1,000 F./2 hr. Vacuum hot-pressed 1.0% 0 M28 2200 F./4 min., o.q.; tempered 66. 5 6, 7, 8 (average, 7)

1 Test specimens cut radially from 5 inch diameter slice of bars 61-338 and compact 300-54.

son of FIGS. 1A and 1B with FIG. 2 that the carbides formed during cooling are noticeably finer in the powder compacts in accordance with the present invention than in the commercial product. This favorable carbide size and distribution of the compact in accordance with the present invention allows it to be heat treated with shorter austenitizing times to achieve full hardness than is the case with commercial material. This is clearly demonstrated by FIG. 3 which shows the effect of austenitizing times at 2200 F. on the as-tempered hardness of the compact of the invention and commercial product. Tempering was effected at 1025 F. for 2+2+2 hours.

The data presented in Table V show that the compact As pointed out above, in rotary cutting tools such as hobs, it is desirable that the hardening treatment produce a uniform size change in the tool diameter so that after hardening the tool is symmetrical or characterized by the substantial absence of out-of-roundness. Because of the absence of preferential carbide alignment as demonstrated hereinabove, the size change of the samples of the compacts in accordance with the invention is much more homogeneous in all directions than that of the commercial sample. As a result, samples in accordance with the invention were substantially symmetrical after a conventional heat hardening treatment, as may be seen from the data presented in Table VII.

TABLE VII.SIZE CHANGE OF VACUUM HOT-PRESSED COMPACT AND COMMERCIAL 1.0% CARBON M2S Diameter expansion, inch NOTE.0.0.R. means Out-ot-Roundness of hardened hob.

1 Hob sample 4% inches O.D.1% inches. I.D.2 inches thick. 2 Austenitize 2,210 F./4 min.; quench into salt at l,200 F./ min., air cool, temper 1,025 I i/2+2 hours.

of the invention exhibits satisfactory properties with respect to response to hardening and tempering, while providing advantage over conventional material with respect to carbide size and distribution, as pointed out hereinabove.

It may be seen from Table VII that the out-of-roundness of the compacted sample was 0.0001; where as, the out-of-roundness of the conventional samples was 0.0011. In the size-change data reported in Table VII, the determinations were made by expressing out-of-roundness as TABLE V.RESPONSE 'IO HARDENING AND 'IIIEQ IOPDEIIILhIT G OFQHOT-COMIACTED AND COMMERCIAL Hardness, R

Austen- Tempered Solidus itizing 1,050 E, hours 'Iemperatempera- After additional heating 2 ture, ture 1 As 2+2 2+2+2 Steel F. F. quenched hours 1,l00 F. 1,150 F. 1,200 F.

1.0% 0 Rex M28 2, 225 63. 5 66. 9 66. 2 65. 5 63. 0 60. 2 2, 275 2, 200 65. 0 66. 4 66. 0 61. 8 59. 0 Vacuum hot-pressed 1.0% 0 M28 compact 1 4 minutes at salt bath temperature. 2 Heated 3 hours each at the indicated temperature.

The photomicrographs of the structures of hot-compacted samples in accordance with the invention presented in FIGS. 4A and 4B may be compared with those of the commercial product shown in FIGS. 5A and 5B. It may be seen that the carbides of FIGS. 4A and 4B are uniformly dispersed, whereas those of FIGS. 5A and 5B exhibit the Well-known directional carbide stringers in a longitudinal section. It should be noted that these structhe ditference between the largest and smallest diameter measurement about the entire circumference of the sample after hardening treatment. The very slight out-of-roundness, e.g., 0.0001, exhibited by the compact sample of the invention may be regarded as no significant size change.

As an example of the excellent response to hardening treatment of compacts in accordance with the present intural differences become even more pronounced in the vention, 3-inch by l-inch thick samples of M28 high speed steel were produced. The samples were compacted by heating to 2140 F. for hours and 2170 F. for 2 hours. The samples were hot pressed with and without the addition of elemental carbon in the form of lampblack in an amount of 0.15%. Prior to compacting the powder was cleaned in chromic acid and dried and screened to 1+325 mesh, -30 mesh particle size distribution. The chemical composition and compacting temperature conditions of the compacts are shown in Table VIII. Specimens were cut from the compacts listed in Table VIII, and such were austenitized in salt, oil quenched and tempered.

(2) Radial tools from a slice of conventionally processed 1% carbon M2S bar having a 5-inch diameter.

All of these M2S tool samples were heat treated (2200 F. for 4 minutes, oil quenched, tempered at 1050" F. for 2+2 hours), surface ground on all sides and then standard tool tip geometry applied to one end.

Table X lists the tool life of the individual tool bits when used to turn steel bars having a hardness of 31 to 32 R and being provided with four /s-it1ch wide slots milled longitudinally into their circumference, 90 apart. In Table X, the average interrupted cut tool life to failure TABLE VIIL-CHEMICAL COMPOSITION OF EIGHT VACUUM HOT PRESSED COMPACTS Chemical composition percent First and second pressing temp. C Mn S 1 A vacuum fusion analysis of the four compacts showed the following gas contents: N, 34 to p.p.m.; O, 15

to 17 p.p.m., and H, 0.3 p.p.m.

2 Prior to testing all compacts were spheroidize annealed as follows: 1,600 F., 2 hour, cooled to 1,400 F., held 6 hours, air cooled to room temperature.

3 Carbon, 0.15% by weight, was added in the form of lampblack to the powder prior to hot pressing.

Table IX lists the as-quenched grain size, average residual carbide size and the hardness after oil quenching from 2200 F. minute to 4 minutes at temperature) and tempering at 1025" F. for 2+2+2 hours. It may be (expressed in number impacts on the unsupported slot edges) is as follows:

(1) 5,440 for compacted tools.

seen that with austenitizing times from 1 to 2 minutes (2) 2,150 for the radial tool from a 5-inch diameter com essentially full hardness is achieved.

mercial bar.

TABLE IX.-RESPONSE TO HARDENING OF FOUR VACUUM HOT PRESSED COMPACTS AND A 5-INCH-DIAMETER BAR FROM A COM- MERCIAL 1.0% C M2S HEAT Average Hardness (R alter residual austenitizing 2,200 F., carbide size, O.Q., tempered microns 1,025 I ./2+2+2 hr.

Carbon, Intercept Maxi 0. 5 1. 0 2.0 4. 0 percent grain size Mean mum min. min. min. min.

1 Slice from a 5 inch diameter conventionally produced bar.

To simulate the expected cutting tool performance of M28 tool steel compacts in accordance with the inven- TABLE X.INTERRUPTED-CUT LIFE OF 1.0 PERCENT CARBON M286 Therefore, the ratio of average tool life of the product of the invention to that of a conventional tool is 2.5 to 1.

LATHE TOOL BITS 1 Tool life, number of impacts at surface cutting speed of ftJniin.

1 Dry turning of a Nu-Die V bar (H13) at R 31-32 with four longitudinal slots 2 inch wide, 90 apart.

2 Tool geometry, 3, 6, 10, 10, 10, 10, 0.030 inch nose radius; inch square tools; iced, 0.010 inch per rev.; depth of out, Mr inch.

3 Tool bits machined from a vacuum hot pressed compact 3inel1es diameter by 1 inch thick.

4 Tool bit machined in a radial direction from the slice of a 5 inch diameter bar (Ref. 1,

tion and conventional MZS tool steel material when manufactured into radial cutters, such as hobs, tool hits were machined in the following materials:

(1) Vacuum hot-pressed compacts of M28 that were heated at 2140 F. plus 2170 F. for 2 hours and have a 3-inch diameter and 1-inch thickness.

Although various embodiments of the invention have been shown and described herein, it is obvious that other adaptations and modifications may be made by those skilled in the art without departing from the scope and spirit of the appended claims.

What is claimed is 1. As an article of manufacture, a metal body constructed of compacted particles of a high speed tool or die steel composition containing a metal component capable of reacting with carbon to form carbides, said reactive metal component being at least one metal selected from the group consisting of titanium, vanadium, molybdenum, zirconium, columbium, tungsten and tantalum each of said particles having carbides of said reactive metal substantially evenly dispersed throughout, said body having a hardness of at least about 58 R and being characterized by size change uniformity upon austenitizing, quenching and tempering.

2. An article as defined in claim 1 wherein the composition of said metal body consists of, in percent, 0.80 to 3.00 carbon, up to 2 manganese, up to 1 silicon, up to 0.5 sulfur, up to 18.0 tungsten, up to 10.0 chromium, up to 12 molybdenum, up to 5 vanadium, up to 12 cobalt and balance iron, with tungsten+molybdenum+chromium +vanadium being equal to at least 10 percent.

3. An article as defined in claim 1 wherein the composition of said metal body consists of, in percent, 0.97 to 1.02 carbon, 0.20 to 0.40 manganese, 0.20 to 0.40 silicon, 0.10 to 0.15 sulfur, 6 to 6.5 tungsten, 4 to 4.5 chromium, 4.75 to 5.25 molybdenum, 1.8 to 2.20 vanadium and balance iron, said article being characterized by a hardness after hardening treatment of at least 64 R 4. An article of manufacture as defined in claim 2, in the form of a hob for use in milling applications.

5. The hob of claim 2 wherein said compacted particles are of a metal composition consisting of, in percent, 0.97 to 1.02 carbon, 0.20 to 0.40 manganese, 0.20 to 0.40 silicon, 0.10 to 0.15 sulfur, 6 to 6.5 tungsten, 4 to 4.5 chromium, 4.75 to 5.25 molybdenum, 1.8 to 2.20 vanadium, and balance iron, said hob having a hardness of at least 64 R 6. An article of manufacture as defined in claim 2 wherein each of said particles having an average size of 2 microns and not exceeding about 5 microns maximum.

References Cited UNITED STATES PATENTS 2,164,198 6/1939 Clements 148126X 3,245,763 4/1966 Ohlsson 29-182.7 3,369,891 2/1968 Tarkan 148126X 3,369,892 2/1968 Ellis 148-l26X 3,450,511 6/1969 Frehn 29-182.8

CARL D. QUARFORTH, Primary Examiner A. J. STEINER, Assistant Examiner U.'S. Cl. X.R. 75203 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,5 1,93 Dated February 9: 97

Gary Steven Inventor(s) It is certified that error appears in the aboveidentified patent and that said Letters Patent are hereby corrected as shown below Table II, change column headed "0, percent" to --Mo, percer same Table, change column headed "Co,M percent" to --Co, percent--;

Table III, under column headed "V", line 5, change "2.00" t --2. 3--;

Table v11, Footnote 2, after "l,200F./" add --5--;

Table VIII, column headed "Annealed hardness R change to "'R Table X, main heading, change "1 2Se" to --M2S--; same Table last column, change "5, 100" to --5,4 +0--;

Claim 5, line 1, change "2" to --4--;

Claim 6 change line 1, change "2" to --l--; same claim, line 2,

havf ng" to --have--,

Signed and sealed this 8th day of June 1971.

(SEAL) Attest:

EDWARD M.FLETCHER, JR. WILLIAM E. SCHUYLER, J Attesting Officer Commissioner of Patent 

